This invention generally relates to chemical compression of gases and more particularly to compression of gas through a temperature swing adsorption apparatus and method using waste heat from a turbogenerator.
Gas powered industrial turbines provide efficient and reliable power with minimum environmental impact. These turbines may use a variety of gaseous fuels, including coal-derived syngas, biomass gas products or natural gas, typically available at relatively low pressures at or near the site. Because the gas must be introduced into the combustion chamber of the turbine at pressures at or above the typical combustion pressure, mechanical gas compressors are commonly used to increase the pressure of the gas before introduction as fuel.
In natural gas powered microturbines (turbogenerators) in the 20 kW to 500 kW range, the gas compressors typically are converted air compressors or refrigerant compressors, also commonly used for small air conditioning systems. These microturbines (turbogenerators) typically require that the pressure of the natural gas be increased from distribution pressure (near 1 atmosphere), above the combustion pressure (about 4 atmospheres) and to as high as 12 atmospheres or more for higher power units. Such mechanical compressors are energy intensive and may consume 7% to 10% of the output power of a typical microturbine turbogenerator at full power and up to 30% at half power. This reduces the system thermal efficiency by the same percentage.
For example, a mechanical compressor mechanically squeezes air from a given volume into a smaller volume, resulting in a higher pressure and temperature. There are many means of accomplishing this (centrifugal, diffusion, piston compression, rotary screw compression, scroll compression, rotary valve (Wankel), involute (gear, gyro), etc.). Notwithstanding their differences, these types of mechanical compressors are designed to increase the gas pressure by the desired pressure ratio and also will increase the temperature, depending on the efficiency of the device. In general, the lower the efficiency, the higher the temperature and the more power will be needed to produce gas flow at the desired pressure.
One type of mechanical compressor currently available is a piston reciprocating compressor, which uses an inlet throttling technique of flow modulation to provide improved low flow power characteristics. In practice, this creates significant vibration leading to poor reliability, poor durability, excessive noise and excessive oil carryover. These characteristics are the result of the reciprocating piston action and the difficulty in balancing that type of machinery in a cost efficient manner.
Other types of mechanical compressors include scroll type and twin screw type compressors, both of which use a direct electric motor drive. In addition to being energy intensive, these rotary type compressors use a bypass method of flow modulation, taxing part power operation by as much as 30%. These types of mechanical compressors are less noisy and more durable than piston reciprocating compressors, but are relatively much more expensive.
As such, a need exists for an improved apparatus and method for compression of gas for use as fuel in a turbine.